From Stirring Incidents in the Life of a British Soldier: An Autobiography by Thomas Faughnan (Picton, Ont.: T. Faughnan, 1891, 1879), page 280:

Barry-down-derry Castle,
County Clare, Ireland, Nov. 10th, 1854.

To Timothy Doolan,
afore Sebastopol.

Dear Son,—I take up my pin in haste for fear ye'd be kilt or wounded by thim thievin' Rooshans, afore this letther reaches ye.... Seein' that my latther end is drawin' near, I have secured the aforesaid Jim McManus, the best pinsman in the parish, though 'tis I that says it meself, to dhraw out my will afore I depart this mortal life....

In this text I think it is clear that "pin" is a dialectical pronunciation of "pen" and that the "best pinsman in the parish" is the person with the best penmanship.

However, this spelling is very, very rare and perhaps unique to this book.

"Pensman" however is much more common, e.g. in this transcript of testimony from 1877:

Q. Can you read and write?
A. I can read my own name, sir.
Q. Can you write your own name?
A. Yes, sir.
Q. Can you write aside from being able to write your own name?
A. I don't claim myself to be much of a pensman....
Q. I am not asking you whether you are a good pensman. I am a miserable pensman myself. Can you write anything other than your own name? ....

So it is clear that both literate and illiterate people knew the word.